Diabetic retinopathy, the retinal vascular disease secondary to diabetes, is a leading cause of adult blindness. Today, treatment is relatively successfully aimed retarding the progress and limiting the severe stages of proliferative retinopathy, which is associated with high risk for blindness. With success of these treatments, attention is moving to therapies (e.g., aspirin, aldose reductase inhibitors, tight diabetic control) which might eliminate or reduce the onset of even the mildest forms of retinopathy. Unfortunately, the traditional vision function tests which might be used to monitor the efficacy of any of these treatments often don't show any abnormal vision changes, even after the development of substantial retinopathy. Our laboratory psychophsical tests of vision, particularly of B cone function, show that visual function is often altered prior to development of retinopathy and can be measured easily with clinically viable instrumentation. Further, the earliest sensitivity changes may have a post-receptoral origin and fluctuate with diabetic control. The specific aims of this study are: 1) to relate acute and sustained diabetic blood glucose control in B cone sensitivity measures, 2) establish clear-cut evidence for post-receptoral involvement, as an early sign, with tests which can be adapted to testing clinical patients, 3) correlate local non-foveal retinopathic signs (e.g., capillary non-perfusion) to B cone sensitivity, and 4) use clinical instrumentation measures (BCT) of B cone sensitivity to monitor effects of treatment and change in retinopathic grade in individual diabetics.